1. Field of the Invention
The invention relates to railway rolling stock and consists particularly in a locomotive having three or more trucks constructed to minimize axle-to-axle load transference.
2. The Prior Art
The prior art discloses locomotives having three or more trucks spaced apart lengthwise of the locomotive, as exemplified by C. W. Kell et al. U.S. Pat. No. 2,829,605, in which all of the trucks include truck frames spring supported on a pair of axles and supporting the locomotive underframe by a transversely movable bolster having a swivel connection to the underframe, the end truck bolsters having centering devices such as springs for biasing the bolster to a centered position and thereby maintaining the ends of the locomotive substantially centered transversely of the truck, the intermediate truck bolster or bolsters being arranged for substantially more free play transversely of the truck to permit the center truck or trucks to move outwardly on curved track arcs between the pivot points of the end trucks, even though the center line of the rigid locomotive underframe defines a chord of the same arc. In conventional truck suspensions, such as that of the Kell et al patent, transmission of traction forces at a relatively high level, i.e., at the level of the center plates, such that traction forces applied to the truck at rail level act through a moment arm equal to the height of the underframe bearing plate from the rail tending to tilt the front of the truck upwardly and the rear downwardly, relieving the load on the front axle and increasing the load on the rear axle. Various means have been utilized in the prior art in two truck locomotives for making the effective level of traction force transmission substantially at rail level, as exemplified by Richard L. Lich U.S. Pat. No. 3,547,046, in which a pair of inclined draft links at each side of the truck are arranged so that their projections converge substantially at rail level with their upper ends connected to the locomotive underframe and their lower ends connected by a suitable linkage to a truck part. With such an arrangement, limited lateral movement of the underframe with respect to the truck, desirable for cushioning lateral shocks applied to the wheel flanges by transverse irregularities in the track, can be accommodated through pivotal play in the ends of the links.
Another means utilized in the prior art in two truck locomotives for bringing the level of traction transmission to rail level, as exemplified by Richard L. Lich U.S. Pat. No. 3,693,553, has been to support a truck bolster on the truck frame by means of elastomeric pads supported on the truck frame in longitudinally spaced relation with each other, the pads at each side being inclined longitudinally of the truck in opposite directions such that their normals intersect substantially at rail level. The bolster in turn supports the truck frame on sliding bearings, at least two of which are spaced apart longitudinally of the truck to stabilize the bolster against tipping of the locomotive underframe and a vertically unloaded king pin provides a swivel and traction transmitting connection between the bolster and the underframe. With such an arrangement limited lateral movements of the underframe with respect to the truck for the purpose of cushioning lateral shocks applied to the wheel flanges by transverse irregularities in the track are accommodated through shear transversely of the truck in the bolster mounted elastomeric pads.
In both the link type and elastomeric pad devices for lowering the level of traction force transmission to rail level, sufficient lateral movement of the underframe can be accommodated through the pivotal connections of the links or shear in the pads to cushion the lateral shocks applied to the wheel flanges by the rails, but if such trucks were applied to three-truck locomotives, the much larger transverse excursions required for the intermediate truck during operation on curved track could not be accommodated readily by the pivotal connections of the links or by transverse shear in the bolster supporting pads of the prior art.